The subject invention provides for a thrust measuring test stand for measuring the thrust produced by a jet engine which has been mounted thereon. The thrust measuring test stand includes a base and a floating frame disposed in parallel spaced relationship from said base. The jet engine, the thrust of which is to be measured, is mounted to the floating frame, either on top or underneath the floating frame assembly.
In accordance with the subject invention, the base and floating frame are interconnected by a plurality of elongated support flexures, each of which is provided with first and second elongated generally flat planar webs, with the plane of the first web being orthogonal to the plane of the second web. More specifically, each elongated support flexure consists of a dual I-beam construction wherein the web portion of one I-beam is disposed in orthogonal relationship to the web portion of the other I-beam. The flexures are interconnected between the base and the floating frame such that first web portion of each flexure is disposed in perpendicular relationship to the longitudinal axis of the engine. In operation, the thrust of the jet engine causes a longitudinal movement of the floating frame relative to the base. The movement of the floating frame causes a corresponding bending of the flexure, with the bending being localized in the first web portion of the flexure. More specifically, due to the new and improved dual I-beam construction of the subject flexure, bending of the flexure, which occurs parallel to the longitudinal axis of the engine, is localized in the first web portion of the flexure.
The subject invention further includes a new and improved means for measuring the bending of the web portion, with the transducer of the measuring means being bonded to the first web portion of the flexure. Since bending of the flexure in response to the thrust of the engine is localized in the area where the measuring means is placed, a relatively simple, low cost thrust measuring test stand is provided which can accurately measure the thrust produced by a jet engine.
The design of a jet engine by a manufacturer is accompanied by an estimation of the maximum thrust which will be produced by the engine under optimum operating conditions. In practice, after the construction of a jet engine, both the manufacturer and user require specific data relating to the exact thrust produced by the jet engine under varying conditions. Heretofore, the thrust of a jet engine was measured by affixing the engine on a test stand, with the test stand being supported by flexible support beams. The operation of the engine resulted in movement of the test stand and a corresponding bending of the support beams, with the bending being measured by placing a measuring device, having a plunger-type piston sensor, against the stand. The bending or movement of the stand would actuate the plunger of the calibrated measuring device, with the amount of actuation being proportion to the amount of thrust produced by the engine. A difficulty arose with this type of prior art thrust measurement since a separate calibrated measuring device must be accurately aligned with the test stand to produce accurate results. The necessity of providing highly accurate alignment equipment along with the test stand, resulted in a system which was extremely expensive to manufacture, relatively complicated to operate and of questionable accuracy.
Another difficulty experienced with test stands in the prior art was that vibrations caused by operation of the engine were transmitted to the interface surface at the measuring device. In order to reduce the effect of the vibrations, the prior art test stands were preloaded with additional weight and horizontal forces which inhibited many unwanted vibrations. However, because of the heavy preload, the support beams were required to be relatively strong, thick structures, which were expensive to manufacture, and difficult to align. In addition, measuring errors occurred when using the prior art test stands because bending of the support flexures was not always proportional to the thrust produced by the engine. More specifically, the relatively strong forces applied to the elongated support flexures in the prior art could result in a twisting of the flexure. Further, secondary forces such as a pitching moment would tend to warp the flexures. The resulting warping and twisting of the support flexures introduced errors in the measurement of the thrust.
Accordingly, it is an object of the subject invention to provide a thrust measuring stand which is accurate and which may be produced at substantially reduced manufacturing cost.
It is another object of the subject invention to provide a thrust measuring test stand which includes a new and improved support flexure which functions to localize the bending of the flexure, caused by the operation of the jet engine, in a first web portion to thereby facilitate the measurement thereof.
It is a further object of the subject invention to provide a thrust measuring test stand having new and improved support flexures which are effectively of a dual I-beam construction, with the web portions of the I-beams being disposed in orthogonal relationship to each other, and with one web of an I-beam portion being disposed perpendicular to the longitudinal axis of the engine. By this arrangement, the bending of the flexure is localized in the web portion which is perpendicular to the longitudinal axis of the engine thereby facilitating the measurement of the thrust.
It is still another object of the subject invention to provide a thrust measuring test stand which is provided with a new and improved measuring means bonded to the first web portion of the support flexure.
It is still a further object of the subject invention to provide a thrust measuring test stand having a measuring means, and a new and improved control circuit means which produces an average voltage that is proportional to the thrust produced by the engine, and fractions to cancel and eliminate unwanted secondary forces, such as engine weight.
It is still another object of the subject invention to provide a thrust measuring test stand wherein a new and improved measuring means includes a plurality of transducers bonded to the web portion of the flexures, with the resistance of the transducers varying proportionally to the bending of the webs.
It is still a further object of the subject invention to provide a new and improved thrust measuring test stand, having a floating frame and a base frame, each defined by a generally rectangular, hollow beam member, and wherein a coolant liquid is circulated in and through the hollow beam member to thereby reduce the warping effects of the high temperature produced by the jet engine.